During the Second World War, the FDR administration placed the FBI in charge of political surveillance in Latin America. Through a program called the Special Intelligence Service (SIS), 700 agents were assigned to combat Nazi influence in Mexico, Brazil, Chile, and Argentina. The SIS’s mission, however, extended beyond countries with significant German populations or Nazi spy rings. Marc Becker interrogates a trove of FBI documents from its Ecuador mission to uncover the history and purpose of the SIS’s activities and for the light they shed on leftist organizing efforts in Latin America.